Magnetic material



Patented Sept. 12, 1939 UNITED STATES PATENT. OFFICE 7 My inventionrelates to magnetic material, and more particularly to a material whichcan be very readily powdered, and to magnetic cores and MAGNETICMATERIAL No Drawing.

Application October 21, 1937, Se-

rial No. 170,302. In Germany November 13, 936

the like made from such powder.

To be suitable for the manufacture of powder or mass cores, a materialmust have the following main properties: (1) It must be very brittle sothat it can be readily powdered, (2) it must have a low coercive forceto insure low hysteresis losses.

ganese.

Coercive 51 Mn Fe tome Percent Percent Percent Oersteds Furthermore, theelectrical resistivity of the material according to the invention isrelatively high, which results in low eddy current losses. For instance,an alloy containing 10% Mn and 8% Si and the remainder iron, has aresistivity of about 1.5x l0 ohms per cubic centimeter.

The properties of the material can be further improved by annealing,after it has been powdered, at a high temperature of for instance 1100C. for one hour. Due to such a heat treatment, which may be effected inan atmosphere of hydrogen or wet hydrogen the internal stresses presentin the grains after the powdering operation are removed, so that a lowcoercive force is retained. Furthermore the material has the favorableproperty of hardly sintering at the above annealing temperature,whereas, impurities which afiect the coercive force, such as carbon, areexpelled from the material due to the annealing operation. After theabove heat treatv ment an alloy containing 10% Mn, 8% Si, had a coerciveforce of about 0.08 Oersted. In making a magnetic core, the powderedmaterial may be insulated in a suitable manner, for instance by coatingthe particles with a layer of zinc am- 2 Claims. (01. -123) moniumphosphate, mixed with a binder. Subsequently the material is pressedinto cores of the desired shape. Such, cores have very low hysteresisand eddy current losses and thus are very advantageous in themanufacture of coils 5 for high and low frequency purposes.

I first give a complete description of the manner of making a core forhigh frequency purposes.

82 parts (by weight) of commercial iron (con- 10 taining about 0.03% C)with 10 parts of manganese and 8 parts of silicon are melted together ina high frequency furnace and poured out into coquilles in the form oflarge flat plates. These plates are taken from the coquilles when 1|still very hot (about 1200 C.) and thrown into cold water. V,

After this the material'is very easily crushed to particles measuring nomore than 5 mm. in diameter. The latter are put into a steel ball millthrough which a slow and continuous stream of dry air is passing thuscausing the lightest particles formed during milling to leave the milland settle down in a large glass container. The maximum size of theparticles thus sieved out is about 3011., as shown by the microscope,but the mean size is much smaller.

The powder is mixed with a concentrated ammoniacal solution of ammoniumphosphate (about 10% by weight) from which the excess ammonia and thewater is driven out at a temperature of about C. After this the binder(6% by weight of a Bakelite resin) is added in the usual way.

in which,

or is the eddy current loss factor in ohms per henry per cycle,

Re is the equivalent eddy currentloss resistanc in ohms, 1

L is the self-inductance of the Epstein arrangement in henries, and

f is the frequency in cycles per sec.

For lower frequencies higher permeabilities are as a rule required. Tothat cue the above mentioned process is slightly altered. Instead ofusing an open ball mill a mill is used, which is carefully closed, whilethe 'air content is driven out by C02. After.l2 hours milling the millis opened and the content sieved out by blowing.

Powder material prepared in this way and otherwise similarly to theabove mentioned method was pressed into a ring of square crosssection(thickness 1 cm. outer diameter 5 cm.) and investigated at 1800 cyclesper sec.

The permeability was found to be 24, and the hysteresis factor C11 inohms per henry as ob- Cu is the hysteresis loss factor in ohms perhenry, Rn is the equivalent hysteresis loss resistance in ohms, and

wound upon the core.

The eddy current losses at the above frequency were too small to bemeasured.

The ohmic resistance of the core mass varies between 10 and 10" 0 percubic centimeter, which is very useful in keeping extra losses due tocapacitive currents through the iron core low.

While I have described my invention in connection with specific examplesand applications, I do not wish to be limited thereto but desire theappended claims to be construed as broadly as permissible in view of theprior art.

What I claim is:

1. A magnetic material for use in powder cores and the like consistingof an alloy containing from 7% to 9% silicon, from 6% to l1% manganeseand the remainder iron.

2. A magnetic material for use in powder cores and the like consistingof an alloy containing about 8% silicon, from 6% to 11% manganese, andthe remainder iron.

J ACOB LOUIS SNOEK.

